Active Drainage Systems with Dual-Input Pressure-Driven Valves

ABSTRACT

A pressure-driven valve is disclosed. The valve includes a housing and a flow control portion disposed within the housing. The housing includes a fluid inlet and a fluid outlet. The flow control portion has a first side subject to fluid flow pressure in a fluid flow channel, and a second side subject to an outlet pressure representative of pressure at the fluid outlet. The flow control portion is deformable to increase and decrease flow through the fluid flow channel based on pressure differentials between the fluid flow pressure, a tube pressure, and the outlet pressure. In some instances, the flow control portion comprises a flow control membrane and a radially-fluctuating pressure tube attached to the periphery of the membrane.

PRIORITY CLAIM

This application claims the benefit of priority of U.S. PatentApplication Ser. No. 61/569,976 titled “ACTIVE DRAINAGE SYSTEMS WITHDUAL-INPUT PRESSURE-DRIVEN VALVES,” filed on Dec. 13, 2011, whoseinventor is Leslie A. Field, which is hereby incorporated by referencein its entirety as though fully and completely set forth herein.

BACKGROUND

The present disclosure relates generally to valves and associatedsystems and methods for use in ophthalmic treatments. In some instances,embodiments of the present disclosure are configured to be part of anIOP control system.

Glaucoma, a group of eye diseases affecting the retina and optic nerve,is one of the leading causes of blindness worldwide. Most forms ofglaucoma result when the intraocular pressure (IOP) increases topressures above normal for prolonged periods of time. IOP can increasedue to high resistance to the drainage of the aqueous humor relative toits production. Left untreated, an elevated IOP causes irreversibledamage to the optic nerve and retinal fibers resulting in a progressive,permanent loss of vision.

The eye's ciliary body continuously produces aqueous humor, the clearfluid that fills the anterior segment of the eye (the space between thecornea and lens). The aqueous humor flows out of the anterior chamber(the space between the cornea and iris) through the trabecular meshworkand the uveoscleral pathways, both of which contribute to the aqueousdrainage system. The delicate balance between the production anddrainage of aqueous humor determines the eye's IOP.

FIG. 1 is a diagram of the front portion of an eye that helps to explainthe processes of glaucoma. In FIG. 1, representations of the lens 110,cornea 120, iris 130, ciliary body 140, trabecular meshwork 150, andSchlemm's canal 160 are pictured. Anatomically, the anterior segment ofthe eye includes the structures that cause elevated IOP which may leadto glaucoma. Aqueous fluid is produced by the ciliary body 140 that liesbeneath the iris 130 and adjacent to the lens 110 in the anteriorsegment of the eye. This aqueous humor washes over the lens 110 and iris130 and flows to the drainage system located in the angle of theanterior chamber. The angle of the anterior chamber, which extendscircumferentially around the eye, contains structures that allow theaqueous humor to drain. The trabecular meshwork 150 is commonlyimplicated in glaucoma. The trabecular meshwork 150 extendscircumferentially around the anterior chamber. The trabecular meshwork150 seems to act as a filter, limiting the outflow of aqueous humor andproviding a back pressure that directly relates to IOP. Schlemm's canal160 is located beyond the trabecular meshwork 150. Schlemm's canal 160is fluidly coupled to collector channels (not shown) allowing aqueoushumor to flow out of the anterior chamber. The two arrows in theanterior segment of FIG. 1 show the flow of aqueous humor from theciliary bodies 140, over the lens 110, over the iris 130, through thetrabecular meshwork 150, and into Schlemm's canal 160 and its collectorchannels.

One method of treating glaucoma includes implanting a drainage device ina patient's eye. The drainage device allows fluid to flow from theinterior chamber of the eye to a drainage site, relieving pressure inthe eye and thus lowering IOP. These devices are generally passivedevices and do not provide a smart, interactive control of the amount offlow through the drainage tube. In addition, fluid filled blebsfrequently develop at the drainage site. The development of the blebtypically includes fibrosis, which leads to increased flow resistanceand it is generally the case that this resistance increases overtime.This development and progression of fibrosis reduces or eliminates flowfrom the anterior chamber, eliminating the capacity of the drainagedevice to affect IOP.

Some examples of IOP control systems or implants protect againstunder-drainage while simultaneously guarding against over-drainage, andconsequently reduce or eliminate bleb formation and fibrotic changes.The system and methods disclosed herein overcome one or more of thedeficiencies of the prior art.

SUMMARY

In one exemplary aspect, the present disclosure is directed to apressure-driven valve that comprises a housing and a flow controlportion. The housing comprises a fluid inlet and a fluid outlet, and theflow control portion is disposed within the housing. The flow controlportion has a first side subject to fluid flow pressure in a fluid flowchannel, and has a second side subject to an outlet pressurerepresentative of pressure at the fluid outlet. The flow control portionis deformable to increase and decrease flow through the fluid flowchannel based on pressure differentials between the fluid flow pressure,a tube pressure, and the outlet pressure.

In some instances, the flow control portion further comprises a flowcontrol membrane and a radially-fluctuating pressure tube attached tothe periphery of the flow control membrane. The pressure tube comprisesa hollow, flexible, curved tube including a closed end and an open end,and is curved to define a circular space having a first diameter. Thepressure tube is filled with fluid conveying the tube pressure, and isdeformable in response to pressure differentials between the outletpressure and the tube pressure, thereby deforming the fluid flowmembrane to increase and decrease flow through the fluid flow channel.

In another exemplary aspect, the present disclosure is directed to apressure-driven valve for implantation in a patient. The pressure-drivenvalve comprises a housing, a fluid flow channel, a pressure tubedisposed within the housing, and a deformable portion attached to thepressure tube. The housing comprises a fluid inlet and a fluid outlet,and the fluid flow channel extends between the fluid inlet and the fluidoutlet. The pressure tube comprises a hollow, flexible, curved tubeincluding a closed end and an open end, is filled with fluid conveying atube pressure, and is curved to define a circular space having a firstdiameter. The deformable portion defines a portion of the fluid flowchannel and is configured to deform to increase and decrease a size ofthe fluid flow channel to regulate fluid flow from the fluid inlet tothe fluid outlet. The deformable portion is disposed and arranged todeform as a result of pressure differentials between the tube pressure,a fluid flow channel pressure, and an outlet pressure representative offluid pressure at the fluid outlet.

In another exemplary aspect, the present disclosure is directed to anIOP control system for implantation in an eye of a patient. The systemcomprises a drainage tube and a pressure-driven valve system. Thedrainage tube is configured to convey aqueous humor from an anteriorchamber of the eye, and the pressure-driven valve system is in fluidcommunication with the drainage tube. The valve system includes a firstpressure-driven valve and a second pressure-driven valve, and isactuatable in response to pressure differentials and configured tocontrol flow rates of the aqueous humor. The first pressure-driven valveis configured to control flow rates of the aqueous humor along thedrainage tube by shifting in response to the pressure differentialbetween the anterior chamber of the eye and the atmospheric pressureacting on the first valve. The second pressure-driven valve comprises apressure tube attached to the periphery of a flow control membrane, andthe pressure tube comprises a hollow, flexible, curved tube including aclosed end and an open end. The pressure tube is filled with fluidconveying the atmospheric pressure. The second pressure-driven valve isconfigured to control flow rates of aqueous humor along the drainagetube by deforming in response to the pressure differentials between theatmospheric pressure, the pressure in the drainage tube between thefirst and second valves, and the pressure of the drainage site acting onthe second valve.

In another exemplary aspect, the present disclosure is directed to amethod of regulating IOP by adjusting drainage from an anterior chamberof an eye with a membrane valve. The method includes directing fluidthrough a fluid flow passageway extending between a fluid inlet and afluid outlet within the membrane valve. The method also includesmodifying the size of the fluid flow channel through deformation of aflow control membrane attached to a hollow, flexible,radially-fluctuating pressure tube as a result of pressure differentialsbetween a tube pressure, a fluid flow channel pressure, and an outletpressure representative of fluid pressure at the fluid outlet.

Providing actively responsive valves in the IOP control system thatfunction even in the absence of an energy supply may reduce blebformation and subsequent fibrotic changes, and thus significantlyincrease the functional life of the IOP control system.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory innature and are intended to provide an understanding of the presentdisclosure without limiting the scope of the present disclosure. In thatregard, additional aspects, features, and advantages of the presentdisclosure will be apparent to one skilled in the art from the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate embodiments of the devices andmethods disclosed herein and together with the description, serve toexplain the principles of the present disclosure.

FIG. 1 is a diagram of the front portion of an eye.

FIG. 2 is a schematic diagram of an exemplary IOP control systemimplanted in the eye according to one embodiment of the presentdisclosure.

FIG. 3 is a schematic cross-sectional diagram of an exemplarypressure-driven valve in a closed condition according to one embodimentof the present disclosure.

FIG. 4 is a schematic cross-sectional diagram of the pressure-drivenvalve shown in FIG. 3 in an open condition according to one embodimentof the present disclosure.

FIG. 5 is a schematic cross-sectional diagram of another exemplarypressure-driven valve in an open condition according to one embodimentof the present disclosure.

FIG. 6 is a top plan view of an exemplary flow control membrane andexemplary pressure tubes useable in the exemplary pressure-driven valveshown in FIG. 5 according to one embodiment of the present disclosure.

FIG. 7 is a schematic cross-sectional diagram of the exemplarypressure-driven valve shown in FIG. 5 in a closed condition according toone embodiment of the present disclosure.

FIG. 8 is a schematic cross-sectional diagram of another exemplarypressure-driven valve in an open condition according to one embodimentof the present disclosure.

FIG. 9 is a schematic cross-sectional diagram of the exemplarypressure-driven valve shown in FIG. 8 in a closed condition according toone embodiment of the present disclosure.

FIG. 10 is a schematic cross-sectional diagram of an exemplary valvesystem including the exemplary pressure-driven valve shown in FIGS. 6and 7 for use in an exemplary IOP control system according to oneembodiment of the present disclosure.

FIG. 11 is a schematic showing a top plan view of the exemplary valvesystem shown in FIG. 10 for use in an exemplary IOP control systemaccording to one embodiment of the present disclosure.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, instruments, methods, and anyfurther application of the principles of the present disclosure arefully contemplated as would normally occur to one skilled in the art towhich the disclosure relates. In particular, it is fully contemplatedthat the features, components, and/or steps described with respect toone embodiment may be combined with the features, components, and/orsteps described with respect to other embodiments of the presentdisclosure. For simplicity, in some instances the same reference numbersare used throughout the drawings to refer to the same or like parts.

FIG. 2 is a diagram of an exemplary IOP control system 200, including adrainage tube 210, a valve system 220, and a divider 230. The IOPcontrol system 200 is positioned in the eye with one end 270 of thedrainage tube 210 located in the anterior chamber 240 and the oppositeend 280 located outside the anterior chamber 240 in a drainage site 250.

The IOP control system 200 may be positioned within the eye in thesubconjunctival pocket between the conjunctiva and the sclera with theanterior border of the valve system 220 positioned approximately 8-10millimeters posterior to the limbus (the border between the cornea andthe sclera). The IOP control system 200 may be held in place within theeye via anchoring structures, the angle of implantation and surroundinganatomy, or by a spring force or other mechanisms that stabilize the IOPcontrol system 200.

In the embodiment pictured in FIG. 2, three areas of pressure interactwith the IOP sensor system 200: P1, P2, and P3. Pressure area P1reflects the pressure of the anterior chamber 240, pressure area P2reflects the pressure of the drainage site 250 in the subconjunctivalspace (and may reflect bleb pressure), and pressure area P3 reflects areference pressure located remotely from P1 and P2 in a dry location 260(effectively reflecting atmospheric pressure). In some embodiments,pressure area P1 reflects the pressure located in a lumen or tube thatis in fluidic communication with the anterior chamber 240.

The IOP control system 200 responds to the pressure differentialsbetween P1, P2, and P3 to control the valve system 220 and therebycontrol the flow rate of aqueous humor through drainage tube 210. Morespecifically, the various pressure differentials across pressure areasP1, P2, and P3 (P1−P2, P1−P3, P2−P3) drive the valve system 220 anddictate the flow rate of aqueous humor through the drainage tube 210without requiring external power at the valve system 220.

The drainage tube 210 drains aqueous humor from the anterior chamber 240of the eye. The valve system 220 controls the flow of aqueous humorthrough a lumen 215 of the tube 210. In the embodiment shown, thepressure area P1 reflects the pressure in the lumen 215 upstream fromthe valve system 220 and downstream from the anterior chamber 240. Theexpected discrepancy between the true anterior chamber pressure and thatreflected by area P1 when located in a tube downstream of the anteriorchamber 240 (even when located between the sclera and the conjunctiva)is very minimal. For example, Poiseuille's law for pipe flow predicts apressure drop of 0.01 mmHg across a 5-millimeter long tube with a 0.300millimeter inner diameter for a flow rate of 3 microliters per minute ofwater. Therefore, because there is almost no pressure difference betweenthe anterior chamber 240 and the interior of the tube 210 that is influid contact with the anterior chamber 240, pressure area P1effectively reflects the pressure of the anterior chamber 240.

As shown in FIG. 2, the drainage tube 210 may be arranged to shunt fluidfrom the anterior chamber 240 to the drainage site 250, which may be atany of numerous locations within the eye. For example, some tubes 210are arranged to shunt aqueous from the anterior chamber 240 to thesubconjunctival space, thus forming a bleb under the conjunctiva, or,alternatively, to the subscleral space, thus forming a bleb under thesclera. Other tube designs shunt aqueous humor from the anterior chamberto the suprachoroidal space, the supraciliary space, the juxta-uvealspace, or to the choroid, thus forming blebs in those respectivelocations. In other applications, the drainage tube 210 shunts aqueoushumor from the anterior chamber 240 to Schlemm's canal, a collectorchannel in Schlemm's canal, or any of a number of different bloodvessels like an episcleral vein. In some examples, the drainage tube 210even shunts aqueous humor from the anterior chamber 240 to outside theconjunctiva. Each of these different anatomical locations to whichaqueous humor is shunted is an example of a drainage site 250. Otherexamples of a drainage site 250 include, but are not limited to: asubconjunctival space, a suprachoroidal space, a subscleral space, asupraciliary space, Schlemm's canal, a collector channel, an episcleralvein, an uveo-scleral pathway, and other locations.

In some embodiments, a divider 230 separates pressure areas P1 and P2from pressure area P3. Pressure area P2 reflects the pressure at adrainage site 250. As such, pressure area P2 may be located in a pocket,such as a bleb, that generally contains aqueous humor or incommunication with such a pocket, via a tube, for example, and is in awet location. Pressure area P3 is physically separated from bothpressure area P1 and pressure area P2 by divider 230. Divider 230 is aphysical structure that separates and isolates the pressure area P1 andthe wet drainage site 250 of pressure area P2 from the dry location 260of pressure area P3. In some embodiments, the divider 230 includes thephysical components of the valve system 220, such as parts of a housing.Note that the divider 230 may take many forms, such as, but not limitedto, a tube extending pressure area P3 to a remote site or a pocket awayfrom and fluidly independent of the drainage site.

In some embodiments of the present disclosure, the atmospheric pressurearea P3 reflects the pressure in an area in close proximity to the eye,and in one embodiment, the pressure area P3 may reflect the pressure inthe eye under the conjunctiva. In such cases, pressure area P3 reflectsa pressure that can be correlated with atmospheric pressure. Pressurearea P3 may also reflect the pressure of a dry portion 260 of thesubconjunctival space, separate and apart from the drainage site 250.Regardless of location, pressure area P3 is intended to reflect thereference atmospheric pressure in the vicinity of the eye or at theeye's surface.

Generally, IOP is a gauge pressure reading—the difference between theabsolute pressure in the eye (as reflected by P1) and atmosphericpressure (as reflected by P3). Atmospheric pressure, typically about 760mm Hg, often varies in magnitude by 10 mmHg or more depending on weatherconditions or indoor climate control systems. In addition, the effectiveatmospheric pressure can vary significantly—in excess of 100 mmHg—if apatient goes swimming, hiking, riding in an airplane, etc. Such avariation in atmospheric pressure is significant since IOP is typicallyin the range of about 15 mm Hg. Because the pressure area P3 reflectsatmospheric pressure, the difference in pressure between the pressureareas P1 and P3 provides an indication of IOP (the pressure differentialbetween the anterior chamber 240 and the atmospheric pressure). Thus,for accurate control of IOP, it is desirable to have an IOP controlsystem reactive to the pressure differential across the pressure of theanterior chamber (as reflected by P1) and atmospheric pressure in thevicinity of the eye (as reflected by P3). Therefore, in one embodimentof the present disclosure, the IOP control system 200 reacts to thepressure differential across P1 and P3 continuously or nearlycontinuously so that the actual IOP (as P1−P3 or P1−f(P3)) can beresponded to accordingly.

The valve system 220 is connected to the drainage tube 210 and controlsthe flow of aqueous humor through the lumen 215 of the tube 210 from theanterior chamber 240 to the drainage site 250. The valve system 220 isdisposed along, and may form a part of, the drainage tube 210 betweenthe end 270 in the anterior chamber 240 and end 280 at the drainage site250. In some embodiments, the valve system 220 is disposed within thelumen 215 of the drainage tube 210 between the end 270 and the end 280.The valve system 220 is configured to control the flow of fluid throughthe drainage tube 210, and thereby control pressure in the eye,including the IOP. For example, when the IOP is high, the valve system220 may operate to permit increased flow through the drainage tube 210,and when IOP is low, the valve system 220 may operate to decrease theflow through the drainage tube 210. In the embodiment pictured in FIG.2, the valve system 220 is configured to be continuously responsive tovarious pressure differentials (P1−P3 and P2−P3) and control fluid flowto the drainage site 250.

While several complications may arise from elevated IOP, variouscomplications may arise from excessively low IOP as well. For example,hypotony is a complication associated with surgeries that serve to shuntthe aqueous humor from the anterior chamber 240 to a drainage site 250.Hypotony is a dangerous, rapid drop in IOP that can result in severeconsequences, such as choroidal hemorrhage and choroidal detachment.Thus, it is desirable to control the rate of aqueous outflow from theanterior chamber 240 to the drainage site 250 not only to preventunder-drainage of aqueous humor, but also to prevent over-drainage andhypotony. The valve system 220 can respond to the pressure differentialsbetween the pressure areas P1, P2, and P3 to control the flow ratethrough the drainage tube 210.

In an exemplary embodiment of the present disclosure, the pressuredifferential across pressure areas P2 and P3 can control valve system220 so as to prevent the formation of a bleb or control the morphologyof a bleb. One of the problems associated with implant surgery is blebfailure. A bleb can fail due to poor formation or fibrosis. The pressurein the bleb is one factor that determines bleb morphology. As explainedabove, too much pressure can cause a bleb to migrate to an undesirablelocation or can lead to fibrosis. The valve system 220 takes intoaccount the pressure area P2 to control the bleb pressure. In oneembodiment of the present disclosure, the difference between thepressure in the bleb (as reflected by P2) and atmospheric pressure (asreflected by P3) can be used to control valve system 220 to maintain adesirable bleb pressure. In another embodiment of the presentdisclosure, the valve system 220 uses at least one dual-inputpressure-driven valve responding to the pressure differential not onlybetween the fluid (P2) and a reference pressure (P3), but also thepressure differential between two different reference pressures withinthe valve system 220. In this manner, the IOP control system 200 of thepresent disclosure can also be used to properly maintain a bleb. One ofordinary skill in the art will recognize that the IOP control devicesand systems disclosed herein may be modified for use in otherapplications utilizing pressure-driven membrane actuation.

The valve system 220 includes at least one pressure-driven membranevalve that does not require external power or feedback from electronicpressure sensors to operate. The valve is configured to allow or blockaqueous humor flowing through the drainage tube 210 to the drainage site250. In some embodiments, the valve is located downstream of a valve (orvalves) that allows aqueous humor to flow from the anterior chamber 240through the drainage tube 210 in response to pressure differentialsbetween P1 and P3. Thus, in some examples, the valve is located as adownstream valve in a valve array connected in series. In some examples,the valve system 220 may be formed as a part of or utilized in a valvesystem such as those disclosed in related application Ser. No.13/315,329 titled “Active Drainage Systems with Pressure-Driven Valvesand Electronically-Driven Pump” incorporated herein by reference. Thepressure-driven membrane valves disclosed herein may form the downstreamvalves of the valve system in the incorporated application, titled“Active Drainage Systems with Pressure-Driven Valves andElectronically-Driven Pump.”

FIG. 3 illustrates a pressure-driven membrane valve 300 according to oneembodiment of the present disclosure that includes a housing 310 that isdefined by a housing section 312, a housing section 314, and a housingsection 316, which mate with one another to form an enclosure withinwhich various other components of the valve 300 are positioned. Thehousing 310 is divided into a reference chamber 320 and a fluid chamber330. The reference chamber 320 is defined by the housing 310, a flowcontrol membrane portion, such as membrane 340, a membrane 350, and apressure access port 355. The fluid chamber 330 houses a valve seat 360,a fluid flow channel 370, a fluid inlet 380, and a fluid outlet 390. Abiasing member 400 connects the flow control membrane 340 and themembrane 350. The fluid inlet 380, the flow control membrane 340, thebiasing member 400, the membrane 350 are all centrally aligned about acentral axis AA. In alternative embodiments, asymmetrical arrangementsof the components of the valve are contemplated. In the picturedembodiment, the components of the valve 300, including the flow controlmembrane 340 and the membrane 350, are generally circular in geometry.In alternative embodiments, different geometries for the valve arecontemplated, including ovoid and rectangular geometries, for example.In some embodiments, the housing sections are integrally formed.

In the pictured embodiment, the housing 310 is divided into thereference chamber 320 and the fluid chamber 330 by the flow controlmembrane 340 and a shelf 410 of the housing section 314. Here, the shelf410 is generally shaped and configured to form an annular ring extendingcircumferentially from the inner wall of the housing section 314. Theflow control membrane 340 is anchored to the shelf 410 in thisembodiment, while other embodiments use other anchoring or adhesionmethods. The housing section 316 forms the fluid inlet 380 and housingsection 314 forms the valve seat 360 within the fluid chamber 330. Thefluid inlet 380 fluidly connects the drainage tube 210 to the valve 300.The housing sections 312 and 314, and 316 cooperate to form the fluidoutlet 390. The valve seat 360 is positioned between the fluid inlet 380and the fluid outlet 390 such that fluid flows into the fluid inlet 380,through the fluid flow channel 370, and out the fluid outlet 390. Insome embodiments, the entire housing is integrally formed. The housing310 may be constructed of any suitable biocompatible material, providedthe material is able to maintain constructional integrity at highinternal pressures and withstand pressure changes.

The reference chamber 320 is bounded and defined by at least the housingsections 312, 314, the flow control membrane 340, the membrane 350, andthe pressure access port 355. The reference chamber 320 may be incommunication with pressure area P3, which is expected to reflectatmospheric pressure, through the pressure access port 355. In someembodiments, P3 reflects the pressure area of the (relatively) drysubconjunctival space. In alternative embodiments, a plurality ofmembranes using separate reference chambers (and reference chamberpressures) is contemplated for use in the valve 300.

In the embodiments shown, the valve seat 360 is a floor surface of thehousing section 314. The central aperture of the valve seat 360 servesas the entrance to the fluid flow channel 370. The valve seat 360 isshaped and configured such that when the flow control membrane 340 restson the valve seat 360, the valve 300 is in a closed condition. The valveseat 360 is positioned relative to the fluid inlet 380 such that thecentral apertures of the valve seat 360 and the fluid inlet 380 areco-aligned about the central axis AA. Thus, in the embodiment picturedin FIG. 3, the central aperture of the valve seat 360 serves as both theexit of the fluid inlet 380 and the entrance to the fluid flow channel370, and when the flow control membrane 340 rests on the valve seat 360,the valve 300 is in a closed position.

In other embodiments, a boss member may be positioned on the valve seat360 such that the boss member concentrically overlies the fluid inlet380. In these embodiments, the boss member effectively functions as thevalve seat. A boss member may permit increased design flexibility andflow control for the valve 300. Varying the height and other dimensionsof the boss member could affect the amount and rate of fluid flowthrough the valve 300.

The fluid flow channel 370 comprises the circumferential gap that arisesbetween the valve seat 360 and the flow control membrane 340 when theflow control membrane 340 lifts away from the valve seat 360 toward thereference chamber 320. As shown in FIG. 3, when the valve 300 is in aclosed condition and the flow control membrane 340 rests on the valveseat 360, the fluid flow channel 370 is a potential space or gap. Asshown in FIG. 4, the fluid flow channel 370 enlarges to an actual spaceor gap when the flow control membrane 340 lifts off the valve seat 360and the valve 300 is in an open or partially open condition. When thevalve 300 is in an open condition, the fluid flow channel 370 isgenerally a constant height around the annular sealing surface of thevalve seat 360 (i.e., the gap between the valve seat 360 and themembrane 340 is generally uniform) at any given time.

Returning to FIG. 3, the biasing member 400 may be shaped and sized as asolid cylinder having two parallel circular faces 412, 414. The biasingmember 400 extends between the flow control membrane 340 and themembrane 350. In the pictured embodiment, the biasing member 400 issized to have a larger diameter than the diameter of the fluid inlet380. The biasing member 400 fixedly attaches to both the membrane 350and the flow control membrane 340 such that movement of the biasingmember 400 in one direction causes the simultaneous movement of themembrane 350 and the flow control membrane 340 in the same direction.More specifically, the face 412 of the biasing member 400 attaches tothe center of the membrane 350, and the face 414 of the biasing member400 attaches to the center of the flow control membrane 340. In otherembodiments, the biasing member may comprise any of a variety of threedimensional shapes, including cubic or polygonal, for example. In otherembodiments, the biasing member 400 may be sized to have the equivalentdiameter to or a smaller diameter than the fluid inlet 380. The shape ofthe biasing member 400 may be chosen depending upon spatial, pressuredrop, material, and flow rate constraints.

The flow control membrane 340 comprises a flexible, deformable,fluid-tight membrane or diaphragm that provides valve functionality bydeflecting in response to pressure differentials across its two opposingsides. The flow control membrane 340 includes two parallel sides, a side340 a and an opposite side 340 b. The side 340 a faces the referencechamber 320, and consequently conveys the pressure of pressure area P3,which may reflect atmospheric pressure. The side 340 b faces the fluidchamber 330, and in particular the fluid inlet 380, and consequentlyconveys the pressure of pressure area P2 a, which reflects the pressureof the fluid within lumen 215 of the drainage tube 210 located upstreamof the valve 300. The side 340 a of the flow control membrane 340 iscoupled with the face 414 of the biasing member 400 such that movementof the biasing member 400 causes simultaneous and proportional movementof the flow control membrane 340 in the same direction as the biasingmember 400. The side 340 b of the flow control membrane 340 isconfigured to selectively seal against the valve seat 360 and therebyclose the valve 300 when movement of the biasing member 400 issufficient, which is driven by membrane 350, as explained below.Alternatively, the membrane 340 may move sufficiently to partially closethe valve to restrict rather than cut off flow.

As shown in FIG. 3, the flow control membrane 340 is securely held inplace within the housing 310 so that it will not be displaced by theforce of the fluid flowing through the valve 300. In the embodimentpictured in FIG. 3, the flow control membrane 340 is anchored to theshelf 410 of the housing section 314. More specifically, a peripheralzone 420 of the flow control membrane 340 is connected to the undersideof the shelf 410. The housing section 314 and the flow control membrane340 are secured into this arrangement by any of a variety of knownmethods, including adhesive, welding, or mechanical fasteners, forexample. In some embodiments, the movable membrane can be fabricatedintegrally with some or all of the housing features by micromachining orMEMS techniques as are well known in the art using a series of materialdeposition, lithographic patterning and etching steps on suitablesubstrates. As an example, a suitable substrate may use a Si or glasswafer as a starting point, with various spacing layers of Silicon,glass, dielectric, or spin-on materials to form parts of the housing,and a flexible membrane material such as thinned silicon, siliconnitride, compliant metal such as gold, or biocompatible organicmaterials such as Parylene, silicone rubber, PDMS or the like, alone orin combination, in suitable thicknesses and dimensions to yield thedesired performance.

In various other embodiments, the flow control membrane 340 may beanchored anywhere within the housing 310 to separate the housing 310into two distinct chambers, a reference chamber and a fluid chamber. Forexample, some embodiments lack the shelf 410, and the flow controlmembrane is anchored directly to the housing 310. Regardless of how theflow control membrane 340 is secured within the housing 310, at least aportion of the housing 310 is connected to a periphery of the flowcontrol membrane 340 to maintain it in a desired position relative tothe valve seat 360.

The membrane 350 comprises a flexible, deformable, fluid-tight membraneor diaphragm that provides valve functionality by deflecting in responseto pressure differentials across its two opposing sides. The membrane350 is sized to have a diameter significantly larger than the diameterof the flow control membrane 340. The membrane 350 includes two parallelsides, a side 350 a and an opposite side 350 b. The side 350 a faces thedrainage site 250 downstream of the valve 300, and consequently conveysthe pressure of pressure area P2 b, which reflects the pressure of thefluid at drainage site 250 located downstream of the valve 300. The side350 b faces the reference chamber 320, and consequently conveys thepressure of pressure area P3, which may reflect atmospheric pressure.The side 350 b of the membrane 350 is coupled with the face 412 of thebiasing member 400 such that movement of the membrane 350 causessimultaneous and proportional movement of the flow control membrane 340in the same direction as the biasing member 400, and visa-versa. As willbe explained in further detail below, the membrane 350 shifts inresponse to pressure differences between drainage site 250 (downstreamof the valve 300) and the reference chamber 320 to dominate and controlthe movement of the biasing member 400, which influences the open andclosed condition of the valve 300.

The membrane 350 is securely held in place within the housing 310 sothat it will not be displaced by the force of the pressure differentialsacting on the valve 300. In the embodiment pictured in FIG. 3, themembrane 350 is anchored to the housing section 312. More specifically,a peripheral zone 430 of the membrane 350 is connected to the undersideof the housing section 312. The housing section 312 and the membrane 350are secured into this arrangement by any of a variety of known methods,including adhesive, welding, or mechanical fasteners, for example. Themovable membranes 350 and 340 can be fabricated integrally with some orall of the housing features by micromachining or MEMS techniques as arewell known in the art using a series of material deposition,lithographic patterning and etching steps on suitable substrates. As anexample, a suitable substrate may use a Si or glass wafer as a startingpoint, with various spacing layers of Silicon, glass, dielectric, orspin-on materials to form parts of the housing, and a flexible membranematerial such as thinned silicon, silicon nitride, compliant metal suchas gold, or biocompatible organic materials such as Parylene, siliconerubber, PDMS or the like, alone or in combination, in suitablethicknesses and dimensions to yield the desired performance. In otherembodiments, the membrane 350 may be anchored to anywhere on the housing310 provided the membrane 350 separates the reference chamber 320 fromthe drainage site 250 (downstream of fluid flow channel 370). Regardlessof how the membrane 350 is secured on the housing 310, at least aportion of the housing 310 is connected to a periphery of the membrane350 to maintain it in a desired position relative to the flow controlmembrane 340.

In the pictured embodiment, the flow control membrane 340 and themembrane 350 are shaped and configured as substantially planar membraneshaving a circular shape. Other shapes are also contemplated for themembranes 340, 350, including, but not by way of limitation, rectangularor ovoid shapes. The shape of the membranes 340, 350 may be chosendepending upon spatial, pressure drop, material, and flow rateconstraints.

For purposes of practicality, the membranes 340, 350 should be thickenough to be durable and resistant to corrosion and leakage. However,the membranes 340, 350 should also be thin enough to provide thenecessary flexibility and deflection capabilities which are required ina substantially planar membrane designed for use in apressure-responsive IOP control system 200. A preferred thickness of theflow control membrane 340 will depend on the deflection response desiredfor a given pressure and the material chosen. As an example, it may befabricated out of Parylene and may have a thickness ranging from 0.5 μmto 30 μm. The membrane 350 may have a similar thickness and material asmembrane 340, or for the sake of illustrating a different favorablechoice, it could be made of Silicon and have a thickness ranging from0.3 μm to 10 μm. In some embodiments, the membrane includes annularcorrugations. The thickness, material, and diameter of the membranes340, 350, as well as the depth, number, and orientation of thecorrugations, may all affect the cracking pressure of the flow controlmembrane 340.

The valve 300 is configured as a flow control valve that can completelyor partially block the flow of aqueous humor by deflecting the flowcontrol membrane 340 completely or partially across the fluid inlet 380.The housing 310 is configured to connect with drainage tube 210 suchthat deflection of the flow control membrane 340 at least partiallyopens and closes the lumen 215 to the outflow of aqueous humor. Asdescribed above, the position of the flow control membrane 340 relativeto the valve seat 360 determines whether the valve 300 is in an open orclosed condition. When the membrane 340 seals against the valve seat360, the valve 300 is in a closed condition. When the membrane 340deflects away from the valve seat 360, the valve 300 is in an opencondition.

The valve 300 is in fluidic communication with the drainage tube 210 andin communication with P3, which reflects the atmospheric pressure(typically at the relatively dry subconjunctiva). In particular, thefluid inlet 380 fluidly interfaces with the drainage tube 210 proximalto the valve 300 (reflecting pressure area P2 a), the membrane 350interfaces with the drainage site 250 distal the valve 300 (reflectingpressure area P2 b), and the reference chamber 320 interfaces with thedry subconjunctiva (reflecting pressure area P3). The flow controlmembrane 340 extends across the housing 310 to form a sealed separationbetween the reference chamber 320 and the fluid inlet 380, therebycreating an effective separation between pressure areas P3 and P2 a,respectively. Accordingly, as the pressure increases against one side ofthe flow control membrane 340, the pressure increase acts to displacethe flow control membrane 340 and the biasing member 400 in thedirection away from the higher pressure. The fluid inlet 380 conveys thepressure of pressure area P2 a on one side 340 b of the flow controlmembrane 340. The reference chamber 320 conveys the pressure of pressurearea P3 on the opposite side 340 a of the flow control membrane 340.

Similarly, the membrane 350 extends across the housing 310 to form asealed separation between the reference chamber 320 and the drainagesite 250 distal to the valve 300, thereby creating an effectiveseparation between pressure areas P3 and P2 b, respectively.Accordingly, as the pressure increases against one side of the membrane350, the pressure increase acts to displace the membrane 350 and thebiasing member 400 in the direction away from the higher pressure. Thefluid within the drainage site 250 distal to the valve 300 conveys thepressure of pressure area P2 b on one side 350 a of the membrane 350.The reference chamber 320 conveys the pressure of pressure area P3 onthe opposite side 350 b of the membrane 350.

Thus, the valve 300 provides a dual membrane response to pressuredifferentials at least in part because of the attached configuration ofthe biasing member 400, the membrane 350, and the flow control membrane340. The flow control membrane 340 shifts within the housing 310 inresponse to the pressure differential between P2 a and P3, and themembrane 350 shifts in response to the pressure differential between P2b and P3. In particular, and as stated above, the flow control membrane340 deflects within the housing 310 of the valve 300 in response to thepressure differential between the fluid inlet 380 pressure (P2 a)against one side 340 b of the flow control membrane 340 and therelatively dry subconjunctival pressure (P3) against the opposite side340 a of the flow control membrane 340. With respect to the membrane350, the membrane 350 deflects within the housing 310 in response to thepressure differential between the drainage tube pressure distal to thevalve outlet 390 (P2 b) against one side 350 a of the membrane 350 andthe reference chamber pressure (P3) against the opposite side 350 b ofthe membrane 350.

The movement of either of the pressure-driven membranes 340, 350 in onedirection causes the simultaneous movement of the biasing member 400,which moves in the same direction as the moving pressure-drivenmembrane. In the pictured embodiment, the membrane 350 dominates andcontrols the movement of the biasing member 400 because the membrane 350has a significantly larger diameter and surface area than the flowcontrol membrane 340. That is, because force is equivalent to pressuremultiplied by area (F=P×A), the net force on the biasing member 400 maybe calculated as follows (ignoring the thickness of the biasing memberfor the sake of simplicity):

Fnet_(Biasing member)=((P2b−P3)×A _(upper membrane))−((P2a−P3)×A_(lower membrane))).

Thus, the biasing member 400 is mostly driven by the force exerted bythe membrane 350, which has a larger surface area than the flow controlmembrane 340. Consequently, the P2 b:P3 pressure differential across themembrane 350 controls the valve 300 more than the P2 a:P3 pressuredifferential across the flow control membrane 340.

The cracking pressure of a valve generally refers to the minimumpressure differential needed between the inlet and outlet of the valveto lift the membrane off its seat. The cracking pressure of the valve300 is dependent upon both the P2 a:P3 pressure differential across theflow control membrane 340 and the P2 b:P3 differential across themembrane 350, though for the embodiment shown in FIG. 3 the latterdifferential dominates the open/closed condition of valve 300 and thusits cracking pressure. If the pressure distal the valve outlet 390 (P2b) is too high in comparison to the atmospheric pressure (P3), themembrane 350 will deflect toward the reference chamber 320 and push thebiasing member 400 toward the valve seat 360, which pushes the flowcontrol membrane 340 against the valve seat 360 and stops flow throughthe valve 300. Because the larger membrane 350 exerts a greater forceupon the biasing member 400 than the smaller flow control membrane 340,the valve 300 will remain in a closed condition in such a situation evenif the pressure of the incoming fluid (P2 a) is higher by the sameamount in comparison to the atmospheric pressure (P3). That is, even ifthe pressure differential across the flow control membrane 340 is thesame as the pressure differential across the membrane 350, the valve 300will remain closed if the pressure of the drainage site (P2 b) is toohigh in comparison to the atmospheric pressure (P3). This configurationallows the valve 300 to assume a closed condition if the pressure (P2 b)at the drainage site 250, which may be within a bleb, becomes too highwith respect to the atmospheric pressure (P3), reflecting anover-drainage situation. Conversely, this configuration allows the valve300 to assume an open position if the pressure (P2 b) at the drainagesite is low enough with respect to atmospheric pressure (P3) to permitdrainage.

The cracking pressure of the valve 300 is dependent mainly upon theforce exerted by the membrane 350 on the biasing member 400, but is alsoinfluenced by the characteristics of the flow control membrane 340.Therefore, the cracking pressure of the valve 300 is dependent upon thetype, diameter, and stiffness of the flow control membrane 340, thetype, diameter, and stiffness of the membrane 350, the size and shape ofthe biasing member 400, and the nature of the connection between thebiasing member 400 and the membranes 340, 350. Accordingly, the crackingpressure may be preselected by controlling these parameters during themanufacturing or assembly processes. In addition, the surgeon may selecta valve 300 having a particular cracking pressure based on the mostappropriate or desired IOP range for the treatment of a particularcondition.

FIG. 3 illustrates the valve 300 in a closed, flow-blocking position. Inthe situation depicted in FIG. 3, the valve 300 is in a closed positionbecause the pressure differential (P2 b−P3) across the membrane 350 ishigh enough to push the flow control membrane 340 against the valve seat360 and because the pressure differential (P2 a−P3) across the flowcontrol membrane 340 is not exceedingly high. The flow control membrane340 rests on the sealing surface of the valve seat 360, thereby blockingthe flow of aqueous humor from the fluid inlet 380, through the fluidflow channel 370, into the fluid outlet 390, and through the drainagesite 250. The valve system 220 is self-limiting because thepressure-driven valve 300 will not open to allow aqueous humor to draininto the drainage site 250 unless the pressure differential across thevalve 300 overcomes the cracking pressure of the valve 300 or unless thepressure differential (P2 a−P3) across the flow control membrane 340 isexceedingly high.

FIG. 4 illustrates the valve 300 in an open, flow-permitting condition.At least in part because the pressure differential (P2 b−P3) across themembrane 350 is not high enough to cause the membrane 350 to push thebiasing member 400 toward the fluid inlet 380, the flow control membrane340 rises off the valve seat 360 and the valve 300 assumes an opencondition, thereby allowing aqueous humor to flow through the fluid flowchannel 370 from the fluid inlet 380 to the fluid outlet 390 in thedirection of any remaining valves and the drainage site 250. As shown inFIG. 4, a second necessary condition for the valve 300 to be in an open,flow-permitting condition is that the pressure differential (P2 a−P3)across the flow control membrane 340 not be exceedingly negative, astate which is highly unexpected in the embodiment presented. Thisensures that drainage of the aqueous humor occurs through the drainagetube 210 if the drainage site pressure (P2 b) is within a desirablerange (with respect to atmospheric pressure).

In addition, in some embodiments, the flexural resistance of the flowcontrol membrane 340, which is lifted off valve seat 360 in theunpressurized case (i.e., when P2 b=P3=P2 a), increases with greaterdisplacement. Accordingly, in higher pressure situations (referring toP2 b−P3), the valve 300 will assume a more closed condition than inlower pressure situations. The higher the pressure of the fluid withinthe fluid outlet 390 (P2 b) in comparison with the pressure of thereference chamber (P3), and assuming the P2 a:P3 pressure differentialacross the flow control membrane 340 is not exceedingly high, the morethe flow control membrane 340 deflects, thereby reducing the entrance toand the dimensions of the fluid flow channel 370 and allowing smalleramounts of aqueous humor to flow from the fluid inlet 380, across thevalve seat 360, and through the fluid outlet 390. Conversely, the lowerthe pressure of the fluid within the fluid outlet 390 (P2 b) incomparison with the pressure of the reference chamber (P3), and assumingthe P2 a:P3 pressure differential across the membrane 340 is notexceedingly negative, the less the flow control membrane 340 deforms toblock the entrance to the fluid flow channel 370, thereby permittingaqueous humor to enter the fluid flow channel 370.

In another embodiment, the flow control membrane 340 is mechanicallyrelaxed in all positions of the biasing member 400. Thus, in suchembodiments, the flow control membrane 340 mainly serves to separate thereference chamber 320 and the fluid chamber 330 and the resistance ofmotion of biasing member 400 is caused by mechanical tensioning ofmembrane 350 only. These embodiments create a system that more readilyresponds to the difference between P2 b and P3 and is less sensitive tothe difference between P2 a and P3.

FIG. 5 illustrates a pressure-driven membrane valve 500 according toanother embodiment of the present disclosure. The valve 500 does notrequire external power or feedback from electronic pressure sensors tooperate. The valve 500 is configured to allow or block aqueous humorflowing from the anterior chamber 240 through the drainage tube 210 toany subsequent valves within the valve system 220 or to the drainagesite 250. In the embodiment shown in FIG. 5, the pressure-drivenmembrane valve 500 includes a housing 510, reference chamber 515, areference pressure tube 520 a, a reference pressure tube 520 b (notshown in FIG. 5), a valve seat 530, a fluid flow channel 535, a flowcontrol membrane 540, and a boss member 550. In the pictured embodiment,the components of the valve 300 are generally circular in geometry andare generally symmetric about the center line BB. In alternativeembodiments, different geometries for the valve are contemplated,including ovoid and rectangular geometries, for example. In alternativeembodiments, the valve 500 includes any number of reference pressuretubes. For example, in some embodiments, the valve 500 includes only onereference pressure tube.

FIG. 6 illustrates a middle view of a portion of a pressure-drivenmembrane valve 500, showing the interconnection of the referencepressure tube 520 a, the reference pressure tube 520 b, and the flowcontrol membrane 540. In the pictured embodiment, the flow controlmembrane 540 is shaped and configured as a substantially planar membranehaving a circular shape with a diameter. Other shapes are alsocontemplated for the membrane 540, including, but not by way oflimitation, rectangular or ovoid shapes. The shape of the flow controlmembrane 540 may be chosen depending upon spatial, pressure drop,material, and flow rate constraints. The flow control membrane 540 issecurely held in place between the tubes 520 a, 520 b so that it willnot be displaced by the force of the fluid flowing through the valve500.

In the pictured embodiment, the tubes 520 a, 520 b are shaped andconfigured as flexible, hollow tubes having a C-shaped portion 560 and alinear tail portion 570. The C-shaped portion 560 terminates in a closedend 572, and the linear tail portion terminates in an open end 574.Other shapes are also contemplated for the tubes 520 a, 520 b,including, but not by way of limitation, rectangular or ovoid shapes.The shape of the tubes 520 a, 520 b may be chosen to echo the outershape of the flow control membrane 540. In the pictured embodiment, thetubes 520 a, 520 b attach to the periphery of the flow control membrane540 to form a circular configuration having an inner diameter D. Thediameter of the flow control membrane 540 may be larger than thediameter D of the circular configuration of the tubes 520 a, 520 b suchthat the center of the membrane 540 droops to a lower plane than thetubes 520 a, 520 b when at rest. The flow control membrane 540 iscircumferentially attached at its periphery to the tubes 520 a, 520 bsuch that deformation of either of the tubes 520 a, 520 b, whetherpressure-induced or otherwise, causes simultaneous deformation of theflow control membrane 540. The flow control membrane 540 may be attachedto the tubes 520 a, 520 b by any of a variety of known methods,including, but not by way of limitation, welding, adhesive, andmechanical fasteners, and as part of a micromechanical or MEMSfabrication sequence. In the pictured embodiment, only two smallportions 575 a, 575 b of the periphery of the membrane 540 are notattached to either of the tubes 520 a, 520 b. Other embodiments may lackthe portions 575 a, 575 b, or may possess smaller or larger portions 575a, 575 b. The flow control membrane 540 and the tubes 520 a, 520 b willbe more fully described below in relation to FIG. 5.

Returning to FIG. 5, FIG. 5 depicts a cross-sectional view of the valve500 taken along lines 5-5 in FIG. 6, showing the larger environment ofthe flow control membrane 540 and the tube 520 a. The housing 510 formsan enclosure within which various other components of the valve 500,such as the flow control membrane 540, the valve seat 530, and the bossmember 550, are positioned. The housing 510 includes a reference chamber515, a fluid inlet 580, a fluid outlet 590, and the valve seat 530. Invarious embodiments, the valve seat can have a separate narrow raisedarea or can be part of the boss structure as shown. The valve seat 530is positioned between the fluid inlet 580 and the fluid outlet 590 suchthat fluid flows from the fluid inlet 580, through the fluid flowchannel 535, and to the fluid outlet 590. A movable or deformableflap-valve or cantilever 591 may be present within or adjacent to thefluid outlet 590 to prevent backflow into the valve 500. In alternativeembodiments, the housing 510 may be formed of separate sections thatcooperate to anchor the flow control membrane 540 and the tubes 520 a,520 b within the housing 510 and to form the fluid inlet 580 and thefluid outlet 590. The housing 510 may be constructed of any suitablebiocompatible material, provided the material is able to maintainconstructional integrity at high internal pressures and withstandpressure changes.

The reference chamber 515 is bounded and defined by at least the housing510, the flow control membrane 540, and the tubes 520 a, 520 b. Thereference chamber 515 is in communication with pressure area P2 b, whichreflects the fluid pressure of the drainage site 250. In someembodiments, the reference chamber 515 is in communication with thedrainage site 250 directly.

In some embodiments, the valve seat 530 may be a floor surface of thehousing 510. In the pictured embodiment, the boss member 550 ispositioned on the valve seat 530 such that the boss memberconcentrically overlies the fluid inlet 580. It should be noted thatsome contemplated embodiments do not include the boss member 550. In avalve without a boss member, the central aperture of the valve seat 530serves as the entrance to the fluid flow channel 535. In a valve withouta boss member, the valve seat is shaped and configured such that whenthe flow control membrane 540 rests on the valve seat 530, the valve 500is in a closed condition. In some embodiments, the valve seat can be aspecific raised area, not shown here.

In the pictured embodiment in FIG. 5, the valve 500 includes a bossmember 550 shaped and configured as a generally annular or toroidcomponent. The boss member 550 is shaped and configured such that whenthe flow control membrane 540 rests on the boss member 550, the valve500 is in a closed condition. The boss member 550 is positioned over thevalve seat 530 such that the central apertures of the boss member 550and the valve seat 530 are co-aligned about the central axis BB. Theboss member 550 is positioned on the valve seat 530 such that the bossmember 550 effectively functions as the valve seat, albeit at a raisedposition within the housing 500. Thus, in the embodiment pictured inFIG. 5, the central aperture of the boss member 550 serves as both theexit of the fluid inlet 580 and the entrance to the fluid flow channel535, and when the flow control membrane 540 rests on the boss member550, the valve 500 is in a closed position. The boss member 550 canpermit increased design flexibility and flow control for the valve 500.Varying the height and other dimensions of the boss member 550 affectsthe amount and rate of fluid flow through the valve 500. In variousembodiments, the boss member 550 may be configured as an integralextension of the valve seat 530, or may be a separate component. In someexamples, the boss member 550 is an integral portion of the valve seat530 and may be molded or machined at the same time as the valve seat530. For example, the boss member may be fabricated by micromachining orMEMS techniques at the same time, or in processing steps before or afterthe fabrication of the valve seat feature, depending on the exact natureof the fabrication process used (such as whether the process steps usedfor these features are primarily additive or subtractive in nature).

The fluid flow channel 535 comprises the circumferential gap that arisesbetween the boss member 550 (or, in embodiments without a boss member,valve seat 530) and the flow control membrane 540 when the flow controlmembrane 540 deflects away from the boss member 550 toward the referencechamber 520 a. The fluid flow channel 535 is a potential space or gapwhen the flow control membrane 540 rests on the boss member 550 and thevalve 500 is in a closed condition, as shown in FIG. 7. As shown in FIG.4, however, the fluid flow channel 535 enlarges when the flow controlmembrane deflects off the boss member 550 into the reference chamber 515and the valve 500 is in an open condition. When the valve 500 is in anopen condition, the fluid flow channel 535 is generally a constant widtharound the annular sealing surface of the boss member 550 (i.e., the gapbetween the boss member 550 and the membrane 540 is generally uniform)at any given time.

The flow control membrane 540 comprises a flexible, deformable,fluid-tight membrane or diaphragm that provides valve functionality by(1) deflecting in response to pressure differentials across its twoopposing sides, and (2) deforming in response to the pressure-inducedflexion and extension of the tubes 520 a, 520 b. The flow controlmembrane 540 includes two parallel sides, a side 540 a and an oppositeside 540 b. The side 540 a faces the reference chamber 515, andconsequently conveys the pressure of pressure area P2 b. The side 540 bfaces the drainage tube 210 proximal to the valve 500, and in particularthe fluid inlet 580, and consequently conveys the pressure of pressurearea P2 a. The side 540 b of the flow control membrane 540 is configuredto selectively seal against the boss member 550 and thereby close thevalve 500 when the pressure against the side 540 a sufficientlyoutweighs the pressure against the side 540 b. As will be explained infurther detail below, the flow control membrane 540 (1) deflects inresponse to pressure differences between pressure areas P2 a and P2 band (2) deforms in response to the flexion and extension of the tubes520 a, 520 b to at least partially open and close the valve 500 bychanging the dimensions of the fluid flow channel 535. In some casesthis latter effect should dominate the response of the valve to pressuredifferentials.

For purposes of practicality, the flow control membrane 540 should bethick enough to be durable and resistant to corrosion and leakage.However, the membrane 540 should also be thin enough to provide thenecessary flexibility and deflection capabilities which are required ina substantially planar membrane designed for use in apressure-responsive IOP control system 200. A preferred thickness of theflow control membrane 540 will depend on the deflection response desiredfor a given pressure and the material chosen. As an example, themembrane may be fabricated out of Parylene and have a thickness rangingfrom 0.5 μm to 30 μm. As another example, the membrane may be made ofSilicon and have a thickness ranging from 0.3 μm to 10 μm. Note thatthese materials and thickness ranges are not intended to be exclusive.In some embodiments, the membrane includes annular corrugations.Membrane thickness, material, and diameter, in combination with thenumber, placement, and depth of the corrugations, all affect thecracking pressure of the valve 500.

The reference pressure tubes 520 a, 520 b are configured asBourdon-style tubes. The Bourdon tube uses the principle that aflattened tube tends to change to a more circular cross-section whenpressurized, and the strain on the material of the tube is magnified byforming the tube into a C-shape, such that the entire tube tends tostraighten out or extend, elastically, as it is pressurized. In mostBourdon tubes, the tube possesses an open end and a closed end. The openend of the tube is connected to a fluid pressure source and the closedend of the tube is employed to shift an actuating arm or indicating armin a circular path. Bourdon tubes respond to an increase in the fluidpressure within the tube by extending, which results in the closed endof the tube moving in a generally circumferential path which istranslated into the rotational or linear movement of the actuating orindicating arm that may be referred to as radially-fluctuating. In thepresent disclosure, each tube 520 a, 520 b is substantially identicaland incorporates the unique features of this disclosure. For simplicityof description, only one of the tubes (520 a) will be described indetail and it should be understood that the tubes 520 a and 520 b actidentically and in unison.

The reference pressure tubes 520 a, 520 b are anchored to the housing510 such that the flow control membrane 540, which is attached to andsuspended between the tubes 520 a, 520 b, may deflect in oppositedirections toward and away from the fluid inlet 580 within the housing510. The tubes 520 a, 520 b may be anchored within the housing 510 inany of a variety of known methods, provided the anchoring method doesnot interfere with the pressure-induced flexion or extension of theC-shaped portion 560. As mentioned above with reference to FIG. 6, thetube 520 a comprises a hollow, flexible, curvilinear tube that is shapedand configured to include the curved, C-shaped portion 560 and thelinear tail portion 570. The C-shaped portion 560 is fixedly attached tothe periphery of the flow control membrane 540 such thatpressure-induced deformation of the tube 520 a causes simultaneousdeformation of the flow control membrane 540. The linear tail portion570 of tube 520 a extends through the housing 510 such that the open end574 is in communication with pressure area P3, which is expected toreflect atmospheric pressure. Thus, the fluid within the tube 520 aconveys the pressure of pressure area P3 along the length of the tube520 a. In some embodiments, the tube 520 a is in communication with thedry subconjunctiva. In alternative embodiments, the tube 520 ainterfaces with another portion of the eye or to atmospheric pressuredirectly.

The valve 500 is configured as a flow control valve that can completelyor partially block the flow of aqueous humor by deflecting the flowcontrol membrane 540 completely or partially across the fluid inlet 580.The housing 510 is configured to connect with drainage tube 210 suchthat deflection of the flow control membrane 540 at least partiallyopens and closes the lumen 215 to the outflow of aqueous humor. Asdescribed above, the position of the flow control membrane 540determines whether the valve 500 is in an open or closed condition. Whenthe membrane 540 seals against the boss member 550 or an alternativevalve seat feature (only one exemplary valve seat shown), the valve 500is in a closed condition. When the membrane 540 deflects away from theboss member 550, the valve 500 is in an open condition. The flow controlmembrane 540 controls the passage of aqueous humor through the valve 500by (1) deflecting in response to pressure differences between pressureareas P2 a and P2 b and (2) deforming in response to the flexion andextension of the tubes 520 a, 520 b to at least partially open and closethe valve 500 by changing the dimensions of the fluid flow channel 535.

The flow control membrane 540 controls the passage of aqueous humorthrough the valve 500 in part by deflecting in response to pressuredifferences between pressure areas P2 a and P2 b to at least partiallyopen and close the valve 500 by changing the dimensions of the fluidflow channel 535. In particular, the fluid inlet 580 fluidly interfaceswith the drainage tube 210 proximal the valve 500 (reflecting pressurearea P2 a) and the reference chamber 515 interfaces with the drainagesite 250 distal the valve outlet 590 (reflecting pressure area P2 b).The fluid inlet 580 conveys the pressure of pressure area P2 a on oneside 540 b of the flow control membrane 540. The reference chamber 515conveys the pressure of pressure area P2 b on the opposite side 540 a ofthe flow control membrane 540. The flow control membrane 540 and thetubes 520 a, 520 b extend across the housing 510 to form a sealedseparation between the reference chamber 515 and the fluid inlet 580,thereby creating an effective separation between pressure areas P2 b andP2 a, respectively. Accordingly, as the pressure increases against oneside of the flow control membrane 540, the pressure increase attempts todisplace the flow control membrane 540 in the direction away from thehigher pressure. However, as will be explained below, the design intentof valve 500 is such that the size of fluid flow channel 535 isrelatively insensitive to the pressure differential across the membrane.

The flow control membrane 540 controls the passage of aqueous humorthrough the valve 500 in part by deforming in response to the flexionand extension of the tubes 520 a, 520 b to at least partially open andclose the valve 500 by changing the dimensions of the fluid flow channel535. In particular, the C-shaped portion 560 of the tube 520 a flexesand extends in response to changing pressure differentials between thefluid pressure within the tube 520 a (P3) and the pressure outside thetube 520 a (P2 b). When the pressure within the tube 520 a (P3)sufficiently outweighs the pressure outside the tube (P2 b), the closedend 574 of the tube 520 a extends or attempts to uncoil, thereby pullingon the membrane 540 and causing it to stretch and lift off the bossmember 550, which allows fluid to flow from the fluid inlet 580 throughthe valve 500. Conversely, when the pressure outside the tube 520 a (P2b) is relatively high in comparison to the pressure within the tube 520a (P3), the closed end of the tube 520 a flexes or attempts to coil up,thereby relieving the strain on the membrane 540 and allowing its centerto sag onto the boss member 550, which prevents fluid from flowing intothe valve 500.

In the situation depicted in FIG. 5, the valve 500 is shown in an open,flow-permitting condition. The flow control membrane 540 is lifted offthe sealing surface of the boss member 550, thereby allowing the flow ofaqueous humor from the fluid inlet 580 to the fluid outlet 590 andthrough the drainage site 250. A valve 500 having this configuration isdesigned for use in a scenario where the pressure in the fluid in thedrainage site 250 distal to the valve 500 (P2 b) is approximately equalto or just slightly above the pressure in the reference chamber 520 a(P3). For the state shown in FIG. 5, for example, the pressure P2 b isrelatively close to the pressure P3 inside the tube 520 a, so the tube520 a tends to be in an extended or uncoiled condition, which causes theflow control membrane 540 to stretch, become more planar, and lift offthe valve seat 530, thereby allowing aqueous humor to flow through thevalve 500. More specifically, assuming an initial scenario of P2 bsignificantly greater than P3, the closed end 572 of the tube 520 amoves away from the center line BB as the pressure of P2 b becomes lesspressurized and approaches P3, thereby pulling on the membrane 540 andcausing it to stretch and lift off the boss member 550, which allowsfluid to flow from the fluid inlet 580 through the valve 500. Thus, thevalve 500 will generally assume an open condition and permit the passageof aqueous humor into the drainage site 250 if the pressure P2 b at thedrainage site is not overly high in comparison to the atmosphericpressure P3.

FIG. 7 illustrates the valve 500 in a closed, flow-blocking position.The center of the flow control membrane 540 is resting on the sealingsurface of the boss member 550, thereby blocking the flow of aqueoushumor from the fluid inlet 580 to the fluid outlet 590 and through thedrainage site 250. In the situation depicted in FIG. 7, the pressure P2b is significantly higher than the pressure P3 inside the tube 520 a, sothe tube 520 a tends to be in a flexed or coiled condition, which causesthe flow control membrane 540 to relax and the center of the membrane540 to sag onto the boss member, thereby preventing aqueous humor fromentering the valve 500 through the fluid inlet 580. More specifically,the closed end 572 of the tube 520 a moves toward center line BB as thepressure of P2 b rises in comparison to P3, thereby relieving strain onthe membrane 540 and causing it to sag onto the boss member 550, whichblocks fluid from entering the valve 500. Thus, the valve 500 willgenerally assume a closed condition and partially or completely blockthe passage of aqueous humor into the drainage site 250 if the pressureP2 b at the drainage site is overly high in comparison to theatmospheric pressure P3.

FIG. 8 illustrates a pressure-driven membrane valve 600 according toanother embodiment of the present disclosure. The valve 600 does notrequire external power or feedback from electronic pressure sensors tooperate. The valve 600 is configured to allow or block aqueous humorflowing from the anterior chamber 240 through the drainage tube 210 toany subsequent valves within the valve system 220 or to the drainagesite 250. In the embodiment shown in FIG. 8, the pressure-drivenmembrane valve 600 includes a housing 610, reference chamber 615, areference pressure tube 620 a, a reference pressure tube 620 b (notshown), a valve seat 630, a fluid flow channel 635, a flow controlmembrane 640, and a boss member 650. In the pictured embodiment, thecomponents of the valve 600 are generally circular in geometry. Inalternative embodiments, different geometries for the valve arecontemplated, including ovoid and rectangular geometries, for example.In alternative embodiments, the valve 600 includes any number ofreference pressure tubes. For example, some embodiments may include onlyone reference pressure tube.

The reference pressure tube 620 a, the reference pressure tube 620 b,and the flow control membrane 640 are interconnected in a substantiallyidentical configuration as that shown with respect to the valve 500illustrated in FIG. 6. The reference pressure tubes 620 a, 620 b aresubstantially similar to the reference pressure tubes 520 a, 520 bexcept for the differences noted herein. The flow control membrane 640is shaped and configured as a substantially planar membrane having acircular shape with a diameter D1. Other shapes are also contemplatedfor the membrane 640, including, but not by way of limitation,rectangular or ovoid shapes. The shape of the flow control membrane 640may be chosen depending upon spatial, pressure drop, material, and flowrate constraints. The flow control membrane 640 is securely held inplace between the tubes 620 a, 620 b so that it will not be displaced bythe force of the fluid flowing through the valve 600.

In accordance with the pictured embodiment in FIG. 6, the tubes 620 a,620 b are shaped and configured as flexible, hollow tubes having aC-shaped portion 660 and a linear tail portion 670. The C-shaped portion660 terminates in a closed end 672, and the linear tail portionterminates in an open end 674. Other shapes are also contemplated forthe tubes 620 a, 620 b, including, but not by way of limitation,rectangular or ovoid shapes. The shape of the tubes 620 a, 620 b may bechosen to echo the outer shape of the flow control membrane 640. Thetubes 620 a, 620 b may attach to the periphery of the flow controlmembrane 640 to form a circular configuration having an inner diameterD2. The diameter D1 of the flow control membrane 640 may be larger thanthe diameter D2 of the circular configuration of the tubes 620 a, 620 bsuch that the flow control membrane 640 assumes a curved, concave shapeover the boss member 650.

The flow control membrane 640 is circumferentially attached at itsperiphery to the tubes 620 a, 620 b such that deformation of either ofthe tubes 620 a, 620 b, whether pressure-induced or otherwise, causessimultaneous deformation of the flow control membrane 640. The flowcontrol membrane 640 may be attached to the tubes 620 a, 620 b by any ofa variety of known methods, including, but not by way of limitation,welding, adhesive, and mechanical fasteners. In the pictured embodiment,only two small portions 675 a, 675 b of the periphery of the membrane640 are not attached to either of the tubes 620 a, 620 b. Otherembodiments may lack the portions 675 a, 675 b, or may possess smalleror larger portions 675 a, 675 b. The flow control membrane 640 and thetubes 620 a, 620 b will be more fully described below in relation toFIG. 8. The movable membrane can be fabricated integrally with some orall of the housing features by micromachining or MEMS techniques as arewell known in the art using a series of material deposition,lithographic patterning and etching steps on suitable substrates. As anexample, a suitable substrate may use a Si or glass wafer as a startingpoint, with various spacing layers of Silicon, glass, dielectric, orspin-on materials to form parts of the housing, and a flexible membranematerial such as thinned silicon, silicon nitride, compliant metal suchas gold, or biocompatible organic materials such as Parylene, siliconerubber, PDMS or the like, alone or in combination, in suitablethicknesses and dimensions to yield the desired performance.

Returning to FIG. 8, depicted is a cross-sectional view of the valve 600(as taken along lines 5-5 in FIG. 6), showing the larger environment ofthe flow control membrane 640 and the tube 620 a. The housing 610 formsan enclosure within which various other components of the valve 600,such as the flow control membrane 640, the valve seat 630, and the bossmember 650, are positioned. The housing 610 includes a reference chamber615, a fluid inlet 680, a fluid outlet 690, and the valve seat 630. Thevalve seat 630 is positioned between the fluid inlet 680 and the fluidoutlet 690 such that fluid flows from the fluid inlet 680, through thefluid flow channel 635, and to the fluid outlet 690. In alternativeembodiments, the housing 610 may be formed of separate sections thatcooperate to anchor the flow control membrane 640 and the tubes 620 a,620 b within the housing 610 and to form the fluid inlet 680 and thefluid outlet 690. A movable or deformable flap-valve or cantilever 691may be present within or adjacent to the fluid outlet 690 to preventbackflow into the valve 600. The housing 610 may be constructed of anysuitable biocompatible material, provided the material is able tomaintain structural integrity at high internal pressures and withstandpressure changes.

The reference chamber 615 is defined by at least the housing 610, theflow control membrane 640, and the tubes 620 a, 620 b. The referencechamber 615 is in communication with pressure area P2 b, which reflectsthe fluid pressure of the drainage site 250 distal the valve 600 or thepressure of the drainage site 250. In some embodiments, the referencechamber 615 is in communication with the drainage site 250 directly.

In some embodiments, the valve seat 630 may be a floor surface of thehousing 610 surrounding the fluid inlet 680 and fluid outlet 690. In thepictured embodiment, the boss member 650 is positioned on the valve seat630 such that the boss member overlies the fluid inlet 680 and the fluidoutlet 690. It should be noted that some contemplated embodiments do notinclude the boss member 650. In a valve without a boss member, anaperture 692 of the valve seat 630 serves as the entrance to the fluidflow channel 635 and an aperture 694 of the valve seat 650 serves as theexit to the fluid flow channel 635. In a valve without a boss member,the valve seat is shaped and configured such that when the flow controlmembrane 640 relaxes and covers the aperture 692, the valve 600 is in aclosed condition.

In the pictured embodiment in FIG. 8, the valve 600 includes a bossmember 650 shaped and configured as a generally cylindrical componentincluding an aperture 696 aligned with the fluid inlet 680 and anaperture 698 aligned with the fluid outlet 690. The boss member 650 ispositioned over the valve seat 630 such that the apertures 696, 698 ofthe boss member 650 and the apertures 692, 694 of the valve seat 630,respectively, are co-aligned. The boss member 650 is positioned on thevalve seat 630 such that the boss member 650 effectively functions asthe valve seat, albeit at a raised position within the housing 610.Thus, in the embodiment pictured in FIG. 8, the aperture 696 serves asthe entrance to the fluid flow channel 635 and the exit of the fluidinlet 680, and the aperture 698 serves as the exit to the fluid flowchannel 635 and the entrance to the fluid outlet 690. The boss member650 is shaped and configured such that when the flow control membrane640 rests on the boss member 650 to cover the aperture 696, the valve600 is in a closed condition. The boss member 650 permits increaseddesign flexibility and flow control for the valve 600. Varying theheight and other dimensions of the boss member 650 affects the amountand rate of fluid flow through the valve 600. In various embodiments,the boss member 650 may be configured as an integral extension of thevalve seat 630, or may be a separate component. In some examples, theboss member 650 is an integral portion of the valve seat 630 and may bemolded or machined at the same time as the valve seat 630. For someinstances, the boss member may be fabricated by micromachining or MEMStechniques at the same time, or in processing steps before or after thefabrication of the valve seat feature, depending on the exact nature ofthe fabrication process used (such as whether the process steps used forthese features are primarily additive or subtractive in nature). Othershapes are contemplated for the boss member, including, but not be wayof limitation, polygonal, hemispherical, cubic, and ovoid.

The fluid flow channel 635 comprises the gap that arises between theboss member 650 (or, in embodiments without a boss member, valve seat630) and the flow control membrane 640 when the flow control membrane640 shifts off the aperture 696 of the boss member 650. The fluid flowchannel 635 is a potential space or gap when the flow control membrane640 covers the aperture 696 and the valve 600 is in a closed condition,as shown in FIG. 9. As shown in FIG. 8, however, the fluid flow channel635 enlarges when the flow control membrane 640 shifts off the aperture696 and the valve 600 is in an open condition. When the valve 600 is inan open condition, the fluid flow channel 635 is generally a constantheight above the surface of the boss member 650 (i.e., the gap betweenthe boss member 650 and the membrane 640 is generally uniform) at anygiven time.

The flow control membrane 640 comprises a flexible, deformable,fluid-tight membrane or diaphragm that provides valve functionality bystretching in response to the pressure-induced flexion and extension ofthe tubes 620 a, 620 b. In the pictured embodiment of FIG. 8, themembrane 640 is shown stretched over the boss member 650 such that themembrane is slightly domed or bowed over the boss member 650 at rest.The flow control membrane 640 includes two parallel sides, a side 640 aand an opposite side 640 b. The side 640 a faces the reference chamber615, and consequently conveys the pressure of pressure area P2 b. Theside 640 b faces the drainage tube 210 proximal to the valve 600, and inparticular the fluid inlet 680, and consequently conveys the pressure ofpressure area P2 a.

The side 640 b of the membrane 640 includes a generally annular,washer-shaped stiffening element 700 that is fixedly attached to aperipheral zone of the side 640 b. The stiffening element may be made ofsubstantially the same material as the membrane 640, or may be made ofany of a variety of other flexible or semi-flexible materials. In someembodiments, the stiffening element 700 is less flexible than themembrane 640. In some embodiments, the stiffening element is an integralportion of the membrane 640 and may be molded or machined at the sametime as the membrane 640. In some embodiments, the stiffening elementmay be fabricated by micromachining or MEMS techniques at the same time,or in processing steps before or after the fabrication of the membranefeature, depending on the exact nature of the fabrication process used(such as whether the process steps used for these features are primarilyadditive or subtractive in nature).

In other embodiments, the stiffening element is a separate componentthat is attached to the membrane 640 by any of a variety of knownmethods, including welding, soldering, adhesive, and mechanicalfasteners, by way of non-limiting example. Regardless of how thestiffening element 700 is attached to the membrane 640, the stiffeningelement 700 is configured to move laterally in unison with lateraldeformation (stretching and relaxing) of the membrane 640. For example,when the membrane 640 is stretched laterally, the stiffening element 700will shift laterally outwards (i.e., away from the center of themembrane 640) in unison with the stretching of the membrane 640 becausethe stiffening element is disposed on a peripheral area of the side 640b. Conversely, when the membrane 640 relaxes and/or contracts, thestiffening element 700 will shift laterally inwards (i.e., towards thecenter of the membrane 640) in unison with the relaxation of themembrane 640.

The stiffening element 700 creates a disc-like gap 705 between themembrane 640 and the boss member 650 that maintains the aperture 698 inan open condition. If the aperture 696 is also in an open condition,aqueous humor can flow through the valve 600. The stiffening element 700is configured to selectively seal against the aperture 696 of the bossmember 650 and thereby close or partially close the valve 600. As willbe explained in further detail below, the flow control membrane 640deforms in response to the flexion and extension of the tubes 620 a, 620b to at least partially open and close the valve 600 by stretching tochange the position of the stiffening element 700 relative to theaperture 696 and thereby changing the dimensions of the fluid flowchannel 635. The stiffening element 700 permits increased designflexibility and flow control for the valve 600. Varying the height andother dimensions of the stiffening element 700 affects the amount andrate of fluid flow through the valve 600.

For purposes of practicality, the flow control membrane 640, includingthe stiffening element 700, should be thick enough to be durable andresistant to corrosion and leakage. However, the membrane 640 shouldalso be thin enough to provide the necessary flexibility and deflectioncapabilities which are required in a substantially planar membranedesigned for use in a pressure-responsive IOP control system 200. Apreferred thickness of the flow control membrane 640 will depend on thedeflection response desired for a given pressure and the materialchosen. As an example, it may be fabricated out of Parylene and may havea thickness ranging from 0.5 μm to 30 μm. In other embodiments, themembrane 640 may be made of Silicon and have a thickness ranging from0.3 μm to 10 μm. The stiffening element 700 may be thicker than themembrane 640. For example, the stiffening element 700 may have athickness ranging from 1 μm to 200 μm. As an example, if the membrane isfabricated out of Parylene having a thickness of 3 μm, the stiffeningelement 700 may be made of Parylene having a thickness of 10 μm, or thestiffening element could be made of Silicon and have a thickness rangingfrom 3 μm to 10 μm. In some embodiments, the membrane includes annularcorrugations. Membrane thickness, material, and diameter, in combinationwith the number, placement, and thickness of stiffening elements, andthe number, placement, and depth of corrugations, all affect thecracking pressure of the valve 600.

The reference pressure tubes 620 a, 620 b are configured asBourdon-style tubes, which have been long known in the prior art for themonitoring of fluid pressures, as described above in relation to thevalve 500. As mentioned above, in the present disclosure, each tube 620a, 620 b is substantially identical to the tubes 520 a, 520 b,respectively, except for the differences described herein. Forsimplicity of description, only one of the tubes (620 a) will bedescribed in detail and it should be understood that the tubes 620 a and620 b act identically and in unison.

The reference pressure tubes 620 a, 620 b are anchored to the housing610 such that the flow control membrane 640, which is attached to andsuspended between the tubes 620 a, 620 b, may stretch and relax withinthe housing 610. The tubes 620 a, 620 b may be anchored within thehousing 610 in any of a variety of known methods, provided the anchoringmethod does not interfere with the pressure-induced flexion or extensionof the C-shaped portion 660. Similar to the tube 520 a described abovewith reference to FIG. 6, the tube 620 a comprises a hollow, flexible,curvilinear tube that is shaped and configured to include the curved,C-shaped portion 660 and the linear tail portion 670. The C-shapedportion 660 is fixedly attached to the periphery of the flow controlmembrane 640 such that pressure-induced deformation of the tube 620 acauses simultaneous deformation of the flow control membrane 640. Thelinear tail portion 670 of tube 620 a extends through the housing 610such that the open end 674 is in communication with pressure area P3,which is expected to reflect atmospheric pressure. Thus, the fluidwithin the tube 620 a conveys the pressure of pressure area P3 along thelength of the tube 620 a. In some embodiments, the tube 620 a is incommunication with the dry subconjunctiva. In alternative embodiments,the tube 620 a interfaces with another portion of the eye or toatmospheric pressure directly.

The valve 600 is configured as a flow control valve that can completelyor partially block the flow of aqueous humor by shifting the stiffeningelement 700 of the flow control membrane 640 completely or partiallyacross the aperture 696 to block the fluid inlet 680. The housing 610 isconfigured to connect with drainage tube 210 such that movement the flowcontrol membrane 640 at least partially opens and closes the lumen 215to the outflow of aqueous humor. As described above, the position of theflow control membrane 640, and in particular the position of thestiffening element 700, determines whether the valve 600 is in an openor closed condition. When the membrane 640 relaxes and the stiffeningelement 700 seals against the aperture 696, the valve 600 is in a closedcondition. When the membrane 640 stretches and the stiffening element700 shifts away from the aperture 696, the valve 600 is in an opencondition. The flow control membrane 640 controls the passage of aqueoushumor through the valve 600 by (1) deflecting in response to pressuredifferences between pressure areas P2 a and P2 b, and (2) stretching andrelaxing in response to the extension and flexion of the tubes 620 a,620 b, changing the position of the stiffening element 700 relative tothe aperture 696, and thereby changing the dimensions of the fluid flowchannel 635 to at least partially open and close the valve 600. In somecases this latter effect should dominate the response of the valve topressure differentials.

The flow control membrane 640 controls the passage of aqueous humorthrough the valve 600 in part by stretching and relaxing in response tothe extension and flexion of the tubes 620 a, 620 b, changing theposition of the stiffening element 700 relative to the aperture 696, andthereby changing the dimensions of the fluid flow channel 635 to atleast partially open and close the valve 600. In particular, theC-shaped portion 660 of the tube 620 a flexes and extends in response tochanging pressure differentials between the fluid pressure within thetube 620 a (P3) and the pressure outside the tube 620 a (P2 b). When thepressure outside the tube (P2 b) is approximately equal to or onlyslightly above the pressure within the tube 620 a (P3), the closed end674 of the tube 620 a extends or attempts to uncoil, thereby pulling onthe membrane 640 and causing it to stretch and shift the stiffeningelement 700 off the aperture 696, which allows fluid to flow from thefluid inlet 680 through the fluid flow channel 635. Conversely, when thepressure outside the tube 620 a (P2 b) is relatively high in comparisonto the pressure within the tube 620 a (P3), the closed end of the tube620 a flexes or attempts to coil up, thereby relieving the strain on themembrane 640 and allowing the stiffening element 700 to cover orpartially cover the aperture 696, which blocks or lowers the rate offlow through the valve 600.

In the situation depicted in FIG. 8, the valve 600 is shown in an open,flow-permitting condition. In the pictured embodiment, the components ofthe valve 600 are generally circular in geometry and are generallysymmetric about the center line DD. In alternative embodiments,different geometries for the valve are contemplated, including ovoid andrectangular geometries, for example. In alternative embodiments, thevalve 600 includes any number of reference pressure tubes. For example,in some embodiments, the valve 600 includes only one reference pressuretube.

In FIG. 8, the stiffening element 700 of the flow control membrane 640is shifted off the aperture 696 of the boss member 650, thereby allowingthe flow of aqueous humor from the fluid inlet 680, through the fluidflow channel, to the fluid outlet 690. A valve 600 having thisconfiguration is designed for use in a scenario where the pressure inthe fluid in the drainage site 250 or the drainage tube 210 distal tothe valve 600 (P2 b) is approximately equal to or only slightly abovethe pressure in the reference chamber 620 a (P3). In FIG. 8, forexample, the pressure P2 b is approximately the pressure P3 inside thetube 620 a, so the tube 620 a tends to be in an extended or uncoiledcondition, which causes the flow control membrane 640 to stretchlaterally, and shift the stiffening element laterally off the aperture696, thereby allowing aqueous humor to flow through the valve 600. Morespecifically, assuming an initial scenario of a P2 b significantly aboveP3, the closed end 672 of the tube 620 a moves away from the centerlineDD as the pressure P2 b decreases and becomes approximately equal to P3,thereby pulling on the membrane 640 and causing it to stretch and shiftthe stiffening element 700 off the aperture 696, which allows fluid toflow from the fluid inlet 680 through the valve 600. Thus, the valve 600will generally assume an open condition and permit the passage ofaqueous humor into the drainage site 250 if the pressure P2 b at thedrainage site is not overly high in comparison to the atmosphericpressure P3.

FIG. 9 illustrates the valve 600 in a closed, flow-blocking position.The stiffening element 700 of the flow control membrane 640 is shiftedonto the aperture 696 of the boss member 650, thereby blocking the flowof aqueous humor from the fluid inlet 680 into the fluid flow channel635. In the situation depicted in FIG. 9, the pressure P3 inside thetube 620 a is relatively low compared to the pressure P2 b, so the tube620 a tends to be in an flexed or coiled condition, which causes theflow control membrane 640 to relax, and shift the stiffening elementlaterally onto the aperture 696, thereby blocking the flow of aqueoushumor from entering the valve 600 through the fluid inlet 680. Morespecifically, the closed end 672 of the tube 620 a moves away from thecenterline DD as the pressure of P2 b rises in comparison to P3, therebyrelieving strain on the membrane 640 and causing the stiffening element700 to shift toward the center of the membrane 340 and cover theaperture 696, which blocks aqueous humor from entering the valve 600.Thus, the valve 600 will generally assume a closed condition and blockthe passage of aqueous humor into the drainage site 250 if the pressureP2 b at the drainage site is overly high in comparison to theatmospheric pressure P3.

FIG. 10 is a schematic cross-sectional diagram of an exemplary valvesystem 800 including the exemplary pressure-driven valve 500 shown inFIGS. 6 and 7 for use in an exemplary IOP control system according toone embodiment of the present disclosure. The valve system 800 includestwo pressure-driven membrane valves, a valve 810 and a valve 500,configured to operate in series. The valve 810 controls the entry offluid from the fluid inlet 830 through the valve 810 in response to thepressure differential between the fluid anterior to the valve 810,reflected by P1, and atmospheric pressure, reflected by P3. The valve810 includes a membrane 820 that deflects in response to the pressuredifferential between pressure areas P1 and P3 to allow or block aqueoushumor from flowing from the anterior chamber 240 through the valve 810towards the valve 500. The valve 810 further includes a fluid inlet 830,a fluid outlet 840, and a boss member 850.

The valve 810 may include a secondary path to an override pressurerelief valve (not shown), which may be a membrane valve configured toallow flow at a higher pressure differential than the valve 810. Thissecondary pressure relief valve may be two-staged to guard againstcatastrophic eye depressurization if one stage fails. The pressure areaP2 a reflects the pressure of the fluid flowing from the valve 810towards the valve 500. The pressure area P2 b reflects the pressure ofthe fluid distal the valve 500 or at the drainage site 250. The valve500 may control the entry of fluid from the fluid inlet 580 through thevalve 500 in response to the pressure differential between pressureareas P2 a and P2 b, as well as to the pressure differential betweenpressure areas P2 b and P3. The valve 500 includes the flow controlmembrane 540, the boss member 550, the fluid inlet 580, the fluid outlet590, and the cantilever 591. The cantilever 591 within the fluid outlet590 may function as a check valve to prevent backflow of fluid into thevalve 500. Other embodiments of a valve system according to the presentdisclosure may include the valve 300, the valve 600, or any of a varietyof other dual-input membrane valves instead of or in addition to valve500. The valve system also may include single-membrane valves,electrically controlled valves, or other flow controlling devicesincluding, by way of non-limiting example, valves or pumps.

FIG. 11 is a diagrammatic cross-sectional view of an embodiment of theexemplary valve system 800 shown in FIG. 10 according to the presentdisclosure. FIG. 11 depicts a cross-section through lines 11-11 in FIG.10 showing the valve system 800 including a P1:P3 valve 810 and a P2:P3valve 500. The valve 810 includes the circular flow control membrane820, the fluid inlet 830, four fluid outlets 840, and the boss member850. The fluid inlet 830 is positioned centrally aligned with and underthe membrane 820. The fluid outlets 840 are also positioned under themembrane 820. The valve 500 includes the circular flow control membrane540, the fluid inlet 580, the fluid outlet 590, the cantilever 591, andthe boss member 550. The fluid inlet 580 and the fluid outlet 590 arepositioned under a peripheral portion of the membrane 540. Aqueous humormay flow into the valve 810 through the fluid inlet 830, exit throughthe fluid outlets 840, enter the valve 500 through the fluid inlet 580,and exit through the fluid outlet 590. The cantilever 591 may preventbackflow of aqueous humor into the valve system 800.

Though the pressure-driven valves described in the present disclosureare depicted as comprising disk-like flow control membranes and bossmembers, the valves may be comprised of any of a number of differentflow control elements that meter, restrict, or permit the flow ofaqueous humor from the anterior chamber 240 to the drainage site 250. Insome embodiments, the flow control membranes of the valves described inthe present disclosure may be in contact with a biocompatible gel totransmit pressure from the aqueous humor at a region of interest. Thebiocompatible gel may be one of a variety of biocompatible gels,including silicone dielectric gels used with medical gradepiezoresistive pressure sensors. These modifications prevent theformation of solid fibers as a result of the proteinaceous content ofthe aqueous humor, which could mechanically disrupt valve operation. Inaddition, the pressure-driven valves described herein may be positionedanywhere in fluid communication with the drainage tube 210, whetherwithin or along the drainage tube 210. Moreover, to ensurebiocompatibility, the pressure-driven valves described herein can becoated or encapsulated in a biocompatible material including, but not byway of limitation, polypropylene, silicone, parylene, or other knownbiocompatible materials.

Conventional passive check valves in drainage device implants (e.g., theAhmed Valve) provide a reduced risk of hypotony in the weeks immediatelyfollowing surgery. But these conventional valves have no mechanism foraccounting for drainage site or bleb pressure. The systems disclosedherein may adjust to control flow to the bleb. Accordingly, the systemsand methods disclosed herein provide a device that a) requires zero tominimal power (internal or external), and b) presents a mechanism ofminimizing bleb height (reducing or eliminating bleb) by controlling theflow through the IOP control system 200 based on pressure differentials,which could significantly reduce the effect of fibrosis and also reduceor eliminate other issues related to bleb management.

The systems and methods described herein achieve IOP control with a verysmall device that utilizes zero to very low power. The system takes intoaccount bleb pressure in regulating drainage flow. Accordingly, based onpressure-driven valves and an optional electronic pump to control theflow rate of aqueous humor, the system provides suitable care for apatient suffering from irregular intraocular pressure.

Embodiments in accordance with the present disclosure may be used in avariety of applications to regulate flow and/or pressure. For example,but not by way of limitation, embodiments of the present disclosure maybe utilized to regulate flow and/or pressure as part of amicroanalytical system, a dialysis system, a process control system, adrug delivery system, a solar thermal system, a cooling system, and/or aheating system. In addition, embodiments of the present disclosure maybe utilized to regulate pressure and/or flow in a variety of fluidicsystems such as, but not by way of limitation, the urinary tract, thebrain (e.g., to regulate intracranial pressure), and thecirculatory/renal system (e.g., as part of a dialysis system). Moreover,some embodiments are shaped and configured for implantation in apatient, while others are not.

Persons of ordinary skill in the art will appreciate that theembodiments encompassed by the present disclosure are not limited to theparticular exemplary embodiments described above. In that regard,although illustrative embodiments have been shown and described, a widerange of modification, change, and substitution is contemplated in theforegoing disclosure. It is understood that such variations may be madeto the foregoing without departing from the scope of the presentdisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the presentdisclosure.

We claim:
 1. A pressure-driven valve, comprising: a housing comprising afluid inlet and a fluid outlet; and a flow control portion disposedwithin the housing, the flow control portion having a first side subjectto fluid flow pressure in a fluid flow channel, and having a second sidesubject to an outlet pressure representative of pressure at the fluidoutlet, the flow control portion being deformable to increase anddecrease flow through the fluid flow channel based on pressuredifferentials between the fluid flow pressure, a tube pressure, and theoutlet pressure.
 2. The valve of claim 1, wherein the flow controlportion further comprises: a flow control membrane; and aradially-fluctuating pressure tube attached to the periphery of the flowcontrol membrane, the pressure tube comprising a hollow, flexible,curved tube including a closed end and an open end, the pressure tubebeing filled with fluid conveying the tube pressure, the pressure tubebeing curved to define a circular space having a first diameter, whereinthe pressure tube is deformable in response to pressure differentialsbetween the outlet pressure and the tube pressure, thereby deforming thefluid flow membrane to increase and decrease flow through the fluid flowchannel.
 3. The valve of claim 2, wherein the pressure tube is filledwith fluid conveying an atmospheric pressure.
 4. The valve of claim 3,wherein the flow control portion and the housing are configured torestrict flow when the outlet pressure is substantially higher than theatmospheric pressure.
 5. The valve of claim 2, wherein the flow controlportion further includes a stiffening element, the stiffening elementattached to the flow control membrane on the first side of the flowcontrol portion and configured to shift in response to the deformationof the flow control portion to selectively open and close the valve. 6.The valve of claim 2, wherein the pressure tube is configured to deformin response to the pressure differential between the tube pressure andthe outlet pressure, thereby deforming the flow control membrane from afirst diameter to a second diameter to affect the size of the fluid flowchannel.
 7. A pressure-driven valve for implantation in a patient,comprising: a housing comprising a fluid inlet and a fluid outlet; afluid flow channel extending between the fluid inlet and the fluidoutlet; a pressure tube disposed within the housing, the pressure tubecomprising a hollow, flexible, curved tube including a closed end and anopen end, the pressure tube being filled with fluid conveying a tubepressure, the pressure tube being curved to define a circular spacehaving a first diameter; and a deformable portion attached to thepressure tube, the deformable portion defining a portion of the fluidflow channel and being configured to deform to increase and decrease asize of the fluid flow channel to regulate fluid flow from the fluidinlet to the fluid outlet, the deformable portion being disposed andarranged to deform as a result of pressure differentials between thetube pressure, a fluid flow channel pressure, and an outlet pressurerepresentative of fluid pressure at the fluid outlet.
 8. The valve ofclaim 7, wherein the deformable portion comprises a flow controlmembrane attached at its periphery to the pressure tube and disposedwithin the space, the flow control membrane forming a reference chamberon a first side of the flow control membrane and the fluid flow channelon a second opposing side of the membrane, the reference chamber havingthe outlet pressure, and wherein deformation of the flow controlmembrane increases and decreases the size of the fluid flow channel. 9.The valve of claim 8, wherein the flow control membrane iscircumferentially attached to the pressure tube.
 10. The valve of claim8, wherein the flow control membrane includes corrugations.
 11. Thevalve of claim 8, further including a valve seat positioned within thehousing between the fluid inlet and the fluid outlet, the deformableportion selectively engaging the valve seat to affect flow in the fluidflow channel.
 12. The valve of claim 11, wherein the valve seat is aboss.
 13. The valve of claim 8, wherein the pressure tube is configuredto control flow though the fluid flow channel by deforming in responseto the pressure differential between the tube pressure and the outletpressure, thereby deforming the flow control membrane to selectivelyopen and close the fluid flow channel.
 14. The valve of claim 8, whereinthe flow control membrane is configured to control the fluid flowchannel by deforming in response to the pressure differential betweenthe outlet pressure and the fluid flow channel pressure.
 15. The valveof claim 8, wherein the flow control membrane comprises a flexible,liquid-tight membrane configured to deflect away from a higher pressuretoward a lower pressure in the absence of other forces acting on themembrane.
 16. The valve of claim 8, wherein the pressure tube isconfigured to control flow though the fluid flow channel by deforming inresponse to the pressure differential between the tube pressure and theoutlet pressure, thereby deforming the flow control membrane from afirst diameter to a second diameter to affect the size of the fluid flowchannel.
 17. The valve of claim 8, wherein the flow control membraneincludes a stiffening element disposed on the second opposing side ofthe flow control membrane.
 18. The valve of claim 17, wherein thestiffening element comprises an annular shape.
 19. The valve of claim17, wherein the pressure tube is configured to control flow though thefluid flow channel by deforming in response to the pressure differentialbetween the tube pressure and the outlet pressure, thereby deforming theflow control membrane to shift the position of the stiffening elementrelative to the fluid inlet to selectively open and close the fluid flowchannel.
 20. An IOP control system for implantation in an eye of apatient, comprising: a drainage tube configured to convey aqueous humorfrom an anterior chamber of the eye; and a pressure-driven valve systemin fluid communication with the drainage tube, the valve systemactuatable in response to pressure differentials and configured tocontrol flow rates of the aqueous humor, the valve system including afirst pressure-driven valve and a second pressure-driven valve, whereinthe first pressure-driven valve is configured to control flow rates ofthe aqueous humor along the drainage tube by shifting in response to thepressure differential between the anterior chamber of the eye and theatmospheric pressure acting on the first valve, and wherein the secondpressure-driven valve comprises a pressure tube attached to theperiphery of a flow control membrane, the pressure tube comprising ahollow, flexible, curved tube including a closed end and an open end,the pressure tube being filled with fluid conveying the atmosphericpressure, and wherein the second pressure-driven valve is configured tocontrol flow rates of aqueous humor along the drainage tube by deformingin response to the pressure differentials between the atmosphericpressure, the pressure in the drainage tube between the first and secondvalves, and the pressure of the drainage site acting on the secondvalve.
 21. The system of claim 20, wherein the pressure-driven valvesare arranged in series to operate independently of each other.
 22. Thesystem of claim 20, wherein the flow control membrane comprises aflexible, liquid-tight membrane configured to deflect away from a higherpressure toward a lower pressure in the absence of other forces actingon the membrane.
 23. The system of claim 20, wherein the pressure tubeis curved to define a circular space having a first diameter andcontaining the flow control membrane, and wherein the pressure tube isconfigured to deform in response to the pressure differential betweenpressure of the drainage site and the atmospheric pressure, therebydeforming the flow control membrane to increase and decrease flowthrough the second valve.
 24. The system of claim 23, wherein the secondpressure-driven valve further includes a stiffening element attached tothe flow control membrane and configured to shift in response todeformation of the flow control membrane to selectively open and closethe valve.
 25. The system of claim 23, wherein the flow control membraneis deformable between the first diameter and a second diameter toselectively open and close the fluid flow channel.
 26. A method ofregulating IOP by adjusting drainage from an anterior chamber of an eyewith a membrane valve, comprising: directing fluid through a fluid flowpassageway extending between a fluid inlet and a fluid outlet within themembrane valve; and modifying the size of the fluid flow channel throughdeformation of a flow control membrane attached to a hollow, flexible,radially-fluctuating pressure tube as a result of pressure differentialsbetween a tube pressure, a fluid flow channel pressure, and an outletpressure representative of fluid pressure at the fluid outlet.
 27. Themethod of claim 26, wherein the flow control membrane is attached at itsperiphery to the pressure tube and forms a reference chamber on a firstside of the flow control membrane and the fluid flow channel on a secondopposing side of the membrane, the reference chamber having the outletpressure.
 28. The method of claim 27, wherein modifying the size of thefluid flow channel comprises deforming the pressure tube in response tothe pressure differentials between the tube pressure and the outletpressure, wherein deformation of the pressure tube causes deformation ofthe flow control membrane.